Problem: Solve the equation. $ x - 21 = 6$ $x=$
Explanation: Add $21$ to both sides: x − 21 + 21 x = = 6 + 21 6 + 21 \begin{eqnarray} \\ x - 21 &=& 6 \\ \\ {+21} && {+21} \\\\ x &=& 6 {+ 21} \end{eqnarray} Simplifying, we get: $ x = 27$